1. Field of the Invention
This invention relates to an optical disk apparatus for reproducing and audio/video recording an optical disk such as CD and DVD and a disk drive device incorporated in the apparatus.
2. Description of the Related Art
An optical disk apparatus for reproducing or audio/video recording an optical disk such as CD and DVD incorporates a disk drive device for rotating the optical disk to be read. The disk drive device focuses optical beams on an optical disk surface using an objective lens and creates spots. The smaller size of the spots can realize the higher recoding density of information for the optical disk. The disk drive device, therefore, has a mechanism for reducing the spot size. Namely, the mechanism is prepared which causes the beams from the optical pickup to impinge on the optical disk surface at right angles to prevent coma aberration from being generated.
On the optical disk, tracks with information recorded are formed. Tracking the tracks is carried out by rotation of the optical disk based on the rotation of a turn table and movement of the optical pickup along a guide shaft. The optical disk has warpage and eccentricity. Owing to them, the recorded position of information on the optical disk cannot be tracked exactly by only the above technique. Namely, also where the information recorded position is misaligned by disturbance not predictable, an adjustment mechanism for exactly tracking the position to read the information must be provided.
FIG. 6 is a sectional view of a conventional optical pickup. An objective lens 21 is secured to a lens holder 20. The lens holder 20 is supported by a lens holder supporting portion (not shown) which moves along the guide shaft. The lens holder 20 has a sliding hole 22. The lens holder supporting portion has a shaft 23. With the shaft 23 passing through the sliding hole 22, the lens holder 20 is supported by the lens holder supporting portion.
In the above conventional adjustment mechanism, the lens holder 20 is moved along the extending direction of the shaft 23 so that the spot of a light beam is focused. In addition, the lens holder 20 is made rotatable around the shaft 23 so that the track is aligned two-dimensionally. Specifically, between the lens holder 20 and the lens holder supporting portion, a magnetic driving portion for focusing and another driving portion for tracking are provided. These magnetic portion for focusing and driving portion for tracking constitute the above adjustment mechanism. Generally, on the side of the lens holder 20, a focus coil 25 and a tracking coil (not shown) are loaded, whereas on the side of the lens holder supporting portion opposite to these coils, a permanent magnet (not shown) for focusing and another permanent magnet for tracking are arranged.
By passing a current through the focus coil 25, the lens holder 20 is vertically driven by magnetic force, thereby making the adjustment of focusing of the objective lens 21 attached to the lens holder 20. Likewise, by passing a current through the tracking coil, the lens holder 20 is rotated around the shaft 20, thereby making the adjustment of tracking. By providing the mechanisms for focusing adjustment and for tracking adjustment as described above, even when the information recording position is misaligned owing to the disturbance, deviation of the spot position from the track can be dealt with, thereby permitting the track position to be exactly tracked.
However, a predetermined clearance (e.g. 5 mm) must be provided between the sliding hole 22 of the lens holder 20 and the shaft 23 of the lens holder supporting portion. This clearance will produce wobbling during the movement of the lens holder 20 in the above alignment. An arrow of broken line in FIG. 6 indicates the direction of wobbling. If the wobbling occurs, the jitter is deteriorated to attenuate the quality of information. As a result, the performance of the reproducing apparatus will be attenuated. In order to obviate such inconvenience, in JP-A-2004-164732, two plate-like ferromagnetic bodies are arranged to sandwich the focus coil vertically to make the adjustment of losing magnetic balance so that two positions undergoing magnetic force are located apart from each other.
Further, JP-A-2004-220769 discloses a configuration in which owing to the magnetic suction force acting between a magnetic plate and a magnet, the force in the direction of pushing the bearing segment of the lens holder against its supporting portion acts on the lens holder.